1. Field of the Invention
Although the dental profession has made great strides in alerting the public about the need for regular dental examinations and the profession, through fluoride treatment and improved dental hygiene has lessened the risk of dental caries, many people are still in need of major dental reconstruction. Where, due to illness or poor routine care a tooth has become seriously decayed or through accident a tooth has become damaged, there is still a significant need for tooth reconstruction.
While in past years there may have been a tendency to completely remove a damaged tooth, more modern dental procedure believes that as much of the natural tooth as possible should be saved and preferable repaired. Thus, when the root of the tooth has become exposed through for example serious decay, rather than pulling the tooth, the dentist will attempt to remove as much of the caries as possible. The dentist may also perform root canal treatment on the tooth as part of the treatment. Once the treatment of the decay and/or root damage has been completed, reconstruction of the tooth surface must begin. Then, using various materials, a tooth must be re-formed to provide many years of useful life.
This invention relates generally to the manufacture of artificial tooth reconstructions and more particularly to the application of composite resin to a metal base by means of a superior cohesion layer.
2. Description of the Prior Art
Dental reconstructions comprising a metal base covered with a layer of porcelain are well known. In fact, the use of porcelain in dental reconstruction dates back several hundred years.
However, the porcelain that is used is very abrasive to natural tooth enamel and can cause destruction of the enamel of the teeth opposing the reconstructed surface.
Dentists have found that existing periodontal disease can be aggravated by opposing porcelain dentition. In addition, a porcelain restoration can aggravate peridontal disease associated with the reconstructed tooth. This occurs because the porcelain does not absorb any of the stress produced by action of the opposing dentition against the reconstructed tooth. Another problem associated with porcelain is its tendency to fracture under stress.
Attempts to improve the use of porcelain in teeth have included porcelain fused to metal restorations whereby a particulate suspension of porcelain is applied to a metal alloy. The porcelain is fired in an appropriate furnace and the porcelain is vitrified to the alloy. Porcelain is applied in several layers to achieve the proper appearance so that the restoration matches the other teeth in color.
More recently, there was described in U.S. Pat. No. 4,895,516, the disclosures of which are incorporated herein by reference, a method of manufacturing a resin alloy substructure reinforced dental restoration. The method includes coating the crown and bridge alloy substructure with a porcelain or vitrifiable ceramic. The ceramic is vitrified to fuse the ceramic to the substructure which forms a bonding layer on the substructure. A microporous surface on the ceramic bonding layer is formed with an etching material and thereupon a silane coupling agent is applied to the microporous layer. A polymerizable resin or a composite resin material is placed over the silane coupling agent. Finally, the resin or composite resin material is polymerized.
While such a method may be an improvement over prior methods, it has been found that a superior restoration may be obtained in accordance with the present invention. The present invention eliminates the need for an etching step followed by the use of a silane coupling agent by providing an improved cohesion layer that is absorbent.
Other prior art patents include U.S. Pat. No. 4,654,007 to Sigler and 3,423,831 to Semmelman, the disclosures of which are incorporated herein by reference.
A principal object of the invention is to provide an improved method for securely affixing a composite resin material to the metal base of a reconstruction or crown.
Another object of the invention is to provide a strong chemical bond between the composite resin material and the alloy surface.
Another object of the invention is to provide a dental reconstruction unit or crown which comprises a composite resin material securely bonded to a metal base by means of an intermediate layer, made from the composition of the present invention, such reconstruction unit or crown being more durable and less abrasive than previous units or crowns.
The invention consists of the novel combinations, steps, processes and improvements herein shown and described.